The present invention relates to apparatus for performing hue correction in a digital television receiver.
Hue control in a digital television environment may be performed in a variety of ways. If the sampling clock is phase/frequency locked with the color burst, hue control may be accomplished by adjusting the phase of the sampling clock relative to the phase of the color burst. In this situation phase adjustment may be automatically controlled in response to detecting a chrominance angle signal. An alternate approach is to operate on the chrominance samples directly. For example, the magnitude and angle of the chrominance signal may be generated, the angles modified by correction factors related to the instantaneous chrominance angles, and the magnitude samples multiplied by the sines and cosines of the corrected angles to generate corrected I, (R-Y) and Q, (B-Y) color mixture signals.
A second approach to correcting hue by processing chrominance samples is to develope signals corresponding to the instantaneous phase of the chrominance samples, and in response to these developed signals to generate correction factors representing sin .DELTA..phi. and cos .DELTA..phi. where .DELTA..phi. is the phase change required to produce the desired hue correction. The color mixture signals are then multiplied by the correction factors and the sums of products are formed which correspond to corrected color mixture signals. The sums of products are given by the equations EQU I.sub.n '=I.sub.n cos .DELTA..phi..sub.n +Q.sub.n sin .DELTA..phi..sub.n( 1) EQU Q.sub.n '=Q.sub.n cos .DELTA..phi..sub.n -I.sub.n sin .DELTA..phi..sub.n( 2)
where I.sub.n ', Q.sub.n ' are corrected samples for the instantaneous color mixture signals I.sub.n and Q.sub.n respectively.